The invention relates to a method of manufacturing a fine, monodisperse powder of the binary oxidic compounds of one or more elements of the groups Ib, IIa, IIb, IIIa, IIIb, IVa, IVb, Va, Vb, VIa, VIb, VIIb, VIII of the periodic table as well as of the lanthanides and actinides. The invention further relates to a fine, monodisperse powder of the binary oxidic compounds of one or more elements of the groups Ib, IIa, IIb, IIIa, IIIb, IVa, IVb, Va, Vb, VIa, VIb, VIIb, VIII of the periodic table as well as of the lanthanides and actinides, and to a ceramic composition comprising a fine, monodisperse oxide powder and the use of said powder and composition.
Fine, monodisperse oxide powders are necessary for the manufacture of ceramic compositions for electronic ceramics. The degree of fineness, the size distribution and the purity of the powder particles used are parameters which are crucial for the reactivity and sinterability of the powders. This applies, in particular, to the manufacture of miniaturized, electronic components, for example ceramic capacitors, varistors or actuators having a multilayer structure. Fine, monodisperse powders are also needed to manufacture pastes for screen-printing of ceramic layers in thick-film technology or for providing thin ceramic layers on substrates from colloidal suspensions.
In particular, if only small quantities of oxides must be admixed as dopants with other oxides, the particle size and the degree of dispersion or agglomeration of the powders are of decisive importance to the homogeneous distribution of the dopant in the starting material. It has long been known to those skilled in the art that flawless and reproducible doping in electronic ceramics can only be attained by using fine, monodisperse powders having grain sizes in the micron and sub-micron ranges.
However, great difficulties are attached to the preparation of fine, monodisperse oxide powders having the above-mentioned grain sizes. During calcining a known precursor for oxides, for example carbonates, oxalates, hydroxides, or during spray drying and flash roasting solutions, sols and gels, irregularly shaped aggregates of particles which are composed of numerous crystallites are always formed. When such aggregates are comminuted by grinding, powders having a wide particle size or agglomerate size distribution are obtained, which are rather unsuitable for doping. Besides, in the sub-micron range, monodisperse powders cannot be obtained by classification (sieving, air separation). In addition, abrasion of the grinding members leads to contamination of the powders during grinding. Consequently, sub-micron powders cannot be obtained by reducing the size of the powders, but must be manufactured by means of direct methods. Direct methods include, for example, thermal decomposition in plasma, reaction-spray sintering or gas-phase synthesis. However, these manufacturing technologies require high investments in production facilities.